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ABOUT THIS IMAGE:

This composite radio light image and rendition of our galaxy as seen in
visible light shows enigmatic "high-velocity clouds" of gas high above
the plane of the Milky Way which rain gas into the galaxy, seeding it
with the stuff of stars.

The cloud outlined, and possibly others too, is now known to have low
heavy element content and to be raining down onto the Milky Way disk,
seeding it with material for star birth. Identifying this infalling gas
helps in solving a long-standing mystery of galactic evolution by
revealing a source of the low-metallicity gas required to explain the
observed chemical composition of stars near the Sun.

In this all-sky projection, the edge-on plane of our galaxy appears as
a white horizontal strip. The false-color orange-yellow "clouds" are
regions containing neutral hydrogen, which glows in 21-centimeter
radiation. Hubble Space Telescope's spectrograph was aimed at one of
the clouds (encircled) to measure its detailed composition and
velocity.

This discovery is based on a combination of data from NASA's Hubble
Space Telescope, three radio telescopes (at Effelsberg in Germany, and
Dwingeloo and Westerbork in the Netherlands), the William Herschel
Telescope on the island of La Palma and the Wisconsin H-alpha Mapper
at NOAO's Kitt Peak Observatory.

Object Name: Milky Way

Image Type: Astronomical/Illustration

Photo Credit: Image composite by Ingrid Kallick of Possible Designs, Madison
Wisconsin.
The background Milky Way image is a drawing made at Lund Observatory.
High-velocity clouds are from the survey done at Dwingeloo Observatory
(Hulsbosch & Wakker, 1988).